The invention concerns enclosed miniature motors of the type having an internal rotor and external stator forming a cylindrical air gap, designed as a brushless d.c. motor with the rotor being a permanent-magnet rotor and provided with an axial bearing for the rotor shaft at one axial end face of an external housing for the motor, the rotor shaft projecting out through the external housing's other axial end face, the stator being provided with a winding, and at least the part of the stator which is located radially outwards of the winding to serve as a yoke for conducting flux circumferentially through the stator being formed from a stack of sheet-metal sheets, especially for hand-held dictation devices.
Hitherto there were used in these devices miniature motors with brushes which, on account of extreme, absolutely necessary compactness, exhibit a reduced lifetime resulting from the mechanical commutation. With such devices, strict requirements are placed upon the start-up time, which means that a motor of relatively high power with the lowest possible inertia must be employed.
It is known to employ collectorless direct-current motors where an increased lifetime is used. These motors, especially as the drive in signal-processing devices, were mostly designed as external-rotor motors whose relatively high inertia cannot fulfill the requirement for a start-up time that is as short as possible.